Recently, the performance and functionality of digital cameras and digital movie cameras that use some solid-state image sensor such as a CCD and a CMOS (which will be simply referred to herein as an “image sensor”) have been enhanced to an astonishing degree. In particular, the size of a pixel structure for use in a solid-state image sensor has been further reduced these days thanks to development of semiconductor device processing technologies, thus getting an even greater number of pixels and drivers integrated together in a solid-state image sensor. As a result, the resolution of an image sensor has lately increased rapidly from one million pixels to ten million pixels in a matter of few years. Meanwhile, the higher the density of pixels in an image sensor with such a high resolution, the more complicated its manufacturing process has got to be and the lower the quality of the product should be. On top of that, as it takes a longer time to check out its image quality, the yield and productivity have been affected as well.
The resolution of an image can be increased by not just simply increasing the number of pixels of an image sensor but also shifting the pixels of the image sensor with respect to the image that has been captured by an optical system (which is a so-called “pixel shifting technology”). The pixel shifting technology may be roughly classified into two types. The first type of the pixel shifting technology is spatial shifting, in which the spatial shift is done by arranging a number of pixels in columns and rows on an imaging area of a solid-state image sensor in a shifted pattern so that each row or column of pixels is shifted from its adjacent ones by a half-pixel pitch. On the other hand, the second type of the pixel shifting technology is temporal shifting, in which the temporal shift is done by subtly moving mechanically at least one of a solid-state image sensor with a two-dimensional tetragonal arrangement and the optical system.
An exemplary fundamental principle for making such spatial pixel shifting by slightly changing the spatial positional of an image is disclosed in Patent Document No. 1, in which such a technique for making pixel shifting with the spatial position of the image changed slightly is applied to a three-panel color camera that uses three image sensors. That color camera adopts an arrangement in which image sensor pixels, representing the color green (G) that will achieve high luminous efficacy to the viewer's eyes, are arranged every other row so as to be horizontally shifted from each other by a half pitch, thereby increasing the resolution in the horizontal direction.
Meanwhile, an arrangement in which pixels are shifted not just horizontally but also vertically is disclosed in Patent Document No. 2. Specifically, in the CCD image sensor disclosed in Patent Document No. 2, photosensitive sections associated with the respective pixels have a diamond shape and are arranged in a winding pattern. By arranging the pixels so that they are shifted from each other by a half pixel pitch both horizontally and vertically, the resolution can be increased horizontally and vertically.
As for the temporal pixel shifting technique, an example in which the optical system is subtly moved mechanically with respect to the image sensor is disclosed in Patent Document No. 3, in which a light-transmissive parallel plate is arranged between the image sensor and a lens. By shaking the parallel plate with respect to the optical axis, the optical image produced on the image sensor is moved subtly, thereby increasing the resolution in the direction in which the image is moved subtly. Conversely, a technique for increasing the resolution by moving the image sensor itself subtly instead of the optical system is disclosed in Patent Document No. 4, in which a piezoelectric element is used as a means for moving the image sensor subtly by a half pixel pitch, thereby attempting to increase the resolution.
As described above, according to these conventional pixel shifting techniques, pixels are arranged so as to be shifted from each other by a half pixel pitch both horizontally and vertically or the image sensor is moved subtly by a half pixel pitch both horizontally and vertically, thereby attempting to increase the resolution. Theoretically speaking, if the photosensitive section had an aperture ratio of 100%, the resolution should be doubled by shifting the pixels by a half pitch.